Hibernate / swsusp2 - not quite suspending

OK - i am having some weird issues here - i hope someone can help.

I have tried the test scripts in userui and it all seems to work fine.

the problem I have is that it unpredictably stops suspending and i can't work out why - i can recover it with escape but it just kind of stops - i have used the verbose commands and i see it gets to the activating suspend bit but it never actually does it - but then it does do it sometimes - anyone else getting anything like this?